Model Boat Mayhem
The Shipyard ( Dry Dock ): Builds & Questions => Steam => Topic started by: knoby on February 14, 2009, 03:40:11 pm
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how is everyone controlling their fwd. rev & throttle on valve engines? is there a mixer available that does this?
i have a few ideas myself, but am interested in hearing how you all overcome this problem
cheers Glenn
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If you have a slide or piston valve arrangement engine then the engine itself will obviously have to incorporate it's own reversing mechanism. This reversing mechanism will therefore require an additional servo to operate it. It doesn't need to be proportional of course so one of the On-Off auxilliary gear channels can be used for this purpose.
Speed control in either direction is then controlled by the throttle which operates a steam stop valve in the main supply line. This is usually a ported type of valve that goes from fully open to fully closed within a 90 degree arc of operation and so requires it's own proportional servo. I have not seen any other arrangement other than the two functions being controlled seperately so what you are obviously asking is whether the two servo's can be mixed to operated from a single channel.
The trouble is that the throttle control channel needs to be from zero to full, as an aircraft throttle, but the reversing servo needs to go from one signal to another, reversing it's direction. I'm not sure how this can be achieved with a mixer, which is why I suspect all the ones I have seen so far have used two channels. It will be very interesting to see thought whether anyone has managed to achieve this with a single channel and a mixer.
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Cheddar used to make a magic box that took one servo channel (self-centring) in and produced two outputs, one for the throttle and one for the forward/reverse. I'm lucky in that i have two of them. The result is something which operates like a Morse lever on a full sized cruiser. Otherwise as BB says the obvious way is to use switchable channels. At present as an experiment I'm running my launch and DX6 without the cheddar unit and with a non-self-centring channel for throttle and the two switched channels 5 and 6 as forward and reverse. that means I can have Forward/Neutral/Reverse. I have a slight idea how 2 mixes might be programmed but don't have the DX6 available here ATM.
HTH
Guy
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It depends on the type of radio you have some of the computer ones can be mixed. so its all in one stick.
Proteus,
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thanks for your thoughts guys. i am considering going 2.4 gig for this model, but I'm still not sure if you can programme the throttle stick to work a servo in the same direction when you push the stick up & down.
my other thought was to make a throttle linkage that moves in 1 direction no matter what direction the servo moves from its central position. that would allow me to use a mixer for the throttle & direction servo. i will try to post a picture of what i mean, but its my first attempt at a picture here so it might not come out
the only problem i can foresee with this linkage is getting enough travel to operate the throttle fully from only 45 degrees of servo movement. i guess its possible using longer arms on the servo that the throttle, but will take some experimentation.
cheers Glenn
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opps i was that amazed i got the picture to load that i loaded the wrong 1 lol. hope this makes it clearer
Silly Glenn
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Have a word with Bogstandard who posts on this forum. His 'Engine from Scrap' uses a single servo to control a combined throttle and engine reversing valve.
Regards
Barry M
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Yes Barry but that is an oscillator. They are relatively easy to control with a combined valve as the cylinder porting is equal in both directions so there is no requirement to reconfigue the engine to reverse it. Knoby wants to control a slide valve engine, which is quite a different challenge.
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Yes Barry but that is an oscillator. They are relatively easy to control with a combined valve as the cylinder porting is equal in both directions so there is no requirement to reconfigue the engine to reverse it. Knoby wants to control a slide valve engine, which is quite a different challenge.
did he not also build a Piston valve engine ??? like this
Proteus
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Did I hear my name mentioned?
Oscillating engines and PISTON valve engines (like the one I designed and made above) can be easily controlled by a standard steam control valve. It is just a matter of easily switching the inlet and exhaust ports over.
SLIDE valve engines are a totally different kettle of fish, as they use mechanical means to reverse the engine because of the way the valving system works.
I have only ever played about with slip eccentrics on slide valve engines, and that is no use for your application.
I would suggest if you want to go down the mechanical route, have a word with the flyboys amongst us. They were using all sorts of mechanical mixers for things like elevons well before mixing on radio became the norm, or if someone has built a mechanical mixer for a Kitchen rudder, that might give you a few ideas. But usually they all required the use of two channels and two servos. Usually with one of the servos sliding along a rail, being pushed by another servo.
Have a word with FLJ from Action. They used to produce a fwds/fwds speed controller for water jet boats, with a fully fwds/bwds operation of a servo based around the neutral point, all working from one channel, if that could be modified to give fwds/fwds to a servo instead of a speed controller, it would be perfect for all these slide valve engines. It would allow the models to be controlled from a two channel set rather than multi channel.
IMHO, I would just stick with the two separate channels for operation, one to operate the valve switchover (and if the engine has it, variable valve timing, for economy) and throttle control.
What isn't there can't go wrong.
Bogs
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OK all....just digressing....that funny fluted bit O0 on the steam inlet side was actually a 5/8" UNHLEF.....[left handed] ....four flute multi start tap [goodness that was a mouthful]....that bogstandard converted & brass plated to look like a lubricator
On Paddle ducks :-)) we did some quick calcs %% & concluded the surface area of the lubricator was = to 1/2 of Scotland @ 1:24 scale %% >>:-( <*< <:( 8) ....Derek
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Nice one Derek, I said at the time it was a bit over blinged.
John
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Hi,
I achieved single channel control for forward, neutral, reverse and throttle control with an on-board electronic PIC controller with "home-grown" software - one PWM channel in and two PWM channels out, the neutral deadband being adjustable.
I then changed it back to two channels (no PIC!) , one for direction and the other for throttle, just for the practicality of cruising on the water, slamming into reverse for avoidance (of ducks, other boats, etc) and then forward cruising at the same throttle opening as before the avoidance manoeuvere; it saves trying to find the preferred throttle position again.
Ian
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Hi,
I achieved single channel control for forward, neutral, reverse and throttle control with an on-board electronic PIC controller with "home-grown" software - one PWM channel in and two PWM channels out, the neutral deadband being adjustable.
I then changed it back to two channels (no PIC!) , one for direction and the other for throttle, just for the practicality of cruising on the water, slamming into reverse for avoidance (of ducks, other boats, etc) and then forward cruising at the same throttle opening as before the avoidance manoeuvere; it saves trying to find the preferred throttle position again.
Ian
any chance of some details of the on-board electronic PIC controller ,
thanks Proteus
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Knoby,
Would it be possible to use a (simplified) Geneva wheel, like this link: http://www.flying-pig.co.uk/pages/mechindex.htm (http://www.flying-pig.co.uk/pages/mechindex.htm)
with the 'driver' wheel connected to the steam valve, and the 'driven' wheel connected to your reverser gear. Try to visualise this animation going back-and-forth rather than the continuous input depicted.
The driver will, of course, oscillate as the servo goes from Ahead to Astern, passing through a 'steam OFF' position as the reverser wheel is moving.
I visualise the steam valve as a small-bore gas-tap style with the hole at/near right angles to the ports while the reverser is moving, then gradually opening once the 'gear' is at full travel.
.... it just might work.
Geoff
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thanks for your views guys. i especially like the Geneva wheel idea. I think I'm going to start with separate controls for throttle & direction just to keep it simple for now.
That way i can concentrate on getting the steam plant to work well first , then i can think about playing with the control system for fun.
This week I'm going to fit the water tanks & mount the steam plant, then i can plumb it in. i will take some photos to post so you can all see what Ive been going on about for the last month.
cheers Glenn
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I think that is a sensible approach Glenn. Don't introduce too much complexity until you have proven the reliability of the plant itself first. All radios have auxiliary channels which can easily be used as a reversing controller channel so I'm sure you won't find it too much of an imposition to operate it like that.
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Hi,
Has anyone had problems with servo wear when driving the Stephenson's valve gear. On my Stuart D10, I've noticed some oscillating back-force from the valve gear if I don't clamp the forward / reversing arm as the engine runs. I would imagine that the servo gears and motor might wear under this action.
With regard to my previous posting on this thread on the use of a PIC controller for engine control - it was just a small part of an automatic flash boiler and engine control scheme that I have developed. It was exhibited on the Blackheath stand at the Ally Pally in January, thanks to the kind invitation of Steamboat Phil.
I'm just in the throws of constructing a floating test bed (it dosn't deserve the titlle "boat"!) to run the system on the lake. I think any more detail would required a different thread.
Ian.
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I found the way to stop the servo problem is to eather use a car type servo saver (spring loaded servo arm) or use a 5513120 DB120 CONTROL OVER-RIDE kit, stops the servo straining as long as there is some bounce in the connection the servo is not stalling. I also use this some times with rudders on slower boats but with heavy springs so that if the rudder gets knocked while in transit no damages occurs.
please start a new post with the boiler controle
Proteus
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I have also noticed that the fwd rev lever oscillates on my Gemini engine, although i hadn't given it much thought so far as it isn't fitted into the boat yet.
i am lucky enough to have many servo savers from my car racing days so i will fit 1 to the control servo.
thanks for bringing this point up & thank you Proteus for giving the answer, once again mayhemers to the rescue
Cheers Glenn.
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Hi,
Has anyone had problems with servo wear when driving the Stephenson's valve gear. On my Stuart D10, I've noticed some oscillating back-force from the valve gear if I don't clamp the forward / reversing arm as the engine runs. I would imagine that the servo gears and motor might wear under this action.
With regard to my previous posting on this thread on the use of a PIC controller for engine control - it was just a small part of an automatic flash boiler and engine control scheme that I have developed. It was exhibited on the Blackheath stand at the Ally Pally in January, thanks to the kind invitation of Steamboat Phil.
I'm just in the throws of constructing a floating test bed (it dosn't deserve the titlle "boat"!) to run the system on the lake. I think any more detail would required a different thread.
Ian.
Ian, this system certainly sounds very interesting and I'm sure there would be a lot of members who would like to see you start a new thread on this subject and tell us a bit more abut it.
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Hi Ian,
Welcome to the forum! I tried emailing you after the show (think it was a pm via Paddleducks), but I don't think you received it.
anyhow, this is a great place to show your flash steam system.
miles
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Hi,
I've been progressing with the construction of my flash steam test vessel and identified a requirement for a means of expanding or compressing the normal servo range.
I shall be using my Robbe Navy F14 which has the twin throttle arms. One of the throttle arms is going to be used for controlling the Stevenson valve gear on the Stuart D10 and is required to be in only three positions - neutral, forward and reverse. The other arm is going to control the common drains valve and is only open and closed.
The standard servo has, as you know, only about 90deg movement, whereas the valve gear operating shaft only rotates about 60deg with the neutral somewhere in between, the exact position depending on the slide valve set-up. The drains valve requires about 180deg movement. Both servos are directly coupled to the appropriate valve shaft.
At the weekend, I knocked up a couple of PIC boards to convert the normal ranges to those required. The boards, to be mounted in the boat, have 22-turn pots which are used to adjust for neutral, maximum forward and reverse travel. The forth pot is for adjusting the speed of travel from servo maximum speed down to 30 second per stoke. The fifth pot is a spare for future developement. The board has three servo outputs, one used for the current application and the others for future use (X, Y, Z movement?).
So, the outcome is to be able to operate the throttle levers to their fullest extent knowing that the servos will go to the exact positions.
The photos show the boards with the traditional way of modifying a servo for greater range with external pots, the other photo shows a Compander, as I call it, connected to the valve gear servo.
Ian.
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Hi,
I've finally got my flash steam test vessel in the test tank and have had to make some drastic changes to the valve gear operating servo.
Originally I had a Futaba S3003 servo connected directly to the quadrant operating rod on the Stuart D10 via a brass adaptor collar with four 6BA clamping screws onto the plastic splined shaft of the servo. This worked OK for a while but started slipping even after re-tightening the clamping screws onto the splined shaft. I was also having to over-drive the servo to a stalled conditition to counter-act the back-force previously discussed.
I removed the servo and found the splinning had gone, caused, in part, by the unexpected heat transfer along the rod from the engine.
I forked out for a pair of Futaba S3305s (prompt service from Servoshop) with metal splining and gears, and with three times the torque of the S3003. Since the valve gear quadrant only moves about 45deg and the servo 90deg, I made a linkage to double the torque between the servo and the valve rod (see photos). The linkage also, fortuitously, reduces the heat transfer as well. The other S3305 is used on the very large rudder.
I'm still driving the servo via my Compander PIC as it gives me exact control of the three positions (forward, neutral, reverse) that I need without stalling the servo. The servo instructions specifically says "Do not leave servo stalled"! It also say "Ni-Cad use only" because of the high instantaneous current demand, although I'm using 12A-hr SLA batteries.
The overall setup is very positive in its operation and since, in theory, the servo via its linkage is applying nearly 18 kg-cm torque, there is no back-force movement at all.
In the photos, the servo is located behind the aluminium bulkhead.
Ian.
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Hi,
I should have said the valve gear octant!
Ian.
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With
Has anyone had problems with servo wear when driving the Stephenson's valve gear. On my Stuart D10, I've noticed some oscillating back-force from the valve gear if I don't clamp the forward / reversing arm as the engine runs. I would imagine that the servo gears and motor might wear under this action.
Ian.
I have just made up a slip joint that should eradicate the up and down movement of the lever. It works by having just enough friction to hold the lever steady while in normal running, but when an input from a servo is given, the joint slides to its new position and carries on.
http://madmodder.net/index.php?topic=1054.msg9084#msg9084
The lever has yet to have the holes drilling into it, so that a servo can be connected for operation. That is todays job.
Bogs
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Hi..........what a nice engine,,,,,,,,,,and What a great job you have don to bring it back to life,,,,,,,,first class
regards Bernhard
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Hi Guys,
I thought it might be of help to add a few notes about setting up Stephensons' link equipped engines as it appears that some of you are having issues with this.
Die Slip
One of the most common mistakes made when using/setting up Stephensons' link valve gear is to move the link from one extreme of the link slot to the other when going from forwards to reverse.
Stephensons' link gear, especially on marine engines where the eccentric rods are relatively short, suffers far more from a phenomenon termed ‘DIE SLIP’ where the’ DIE BLOCK’ connecting the ‘VALVE SPINDLE’ to the ‘SLOTTED LINK’ slides sideways in the link slot rather than pushing/pulling the ‘VALVE SPINDLE’.
This occurs because of the extreme angularity imposed on the ‘LINK’ as one eccentric moves towards the link whilst the other is moving away.
This effect is much more severe on a marine type engine where the lengths of the eccentric rods is short, thus making the angular variations between the forward and reverse eccentric rods, and hence the angularity of the ‘LINK’ more severe which in turn presents the 'DIE' to the slot at a much more acute angle… resulting in a sideways movement of the 'DIE' in the 'LINK'.
On a steam locomotive this angularity problem is overcome, to some degree, by fitting the eccentrics to a more rearward axle, often the most rearward, which gives the maximum possible length for the eccentric rods, which in turn reduces the angular variation, but even here some DIE SLIP still occurs.
The way to overcome this is to not use the full length of the available ‘LINK SLOT’ but to restrict the movement to around 90% to 95% of the available slot length in either direction about the centre of the ‘LINK’
This will allow a short length of slot to accommodate the inevitable ‘DIE SLIP’
A properly designed ‘STEPHENSON’S LINK’ gear will have been designed to work at this slot position.
If the full length of slot is used then any ‘DIE SLIP’ will cause the ‘DIE’ to hit the end of the slot as the engine rotates with the result that the whole link assembly, and any connecting levers, will have no option but to move in sympathy thus leading to the perceived, and unwanted, lever movement.
DIE SLIP occurs when the angularity of the LINK relative to the DIE BLOCK is such that the DIE BLOCK will slide sideways in the link arm slot rather than move the VALVE stem in or out.
LOCKING the forward reverse mechanism at the extremes of slot travel, with no available slot length left for ‘DIE SLIP’ will only cause long term damage to the valve operating stem/bearing, and to the sliding die.
It is more usual to set the FULL FORWARDS and FULL REVERSE positions of the valve gear to leave some SLIP space available at the extremes of the LINK SLOT to allow for this DIE SLIP. I.E +/- 90% of available travel.
DIE SLIP is much more of an issue with marine engines since the eccentric rods are generally much shorter than on a locomotive and hence have greater angularity problems to overcome.
Try setting your full forwards and full reverse positions to around 90% of the available slot length in either direction and I think you will find a lot of the perceived problems become much less of an issue.
You will still need to use some form of servo buffering, since there will always be some frictional forces to deal with, but these will not be anything like as extreme as the DIE BOTTOMING out in the LINK.
John,
Lovely work, as always, on the refurbish job…. Is that the ‘MARCHER’ or the ‘BORDERER’ engine, it’s difficult to tell which from the pics, but I suspect the ‘MARCHER’.
Best regards to all. :-)) :-))
AlexC
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It is the Marcher, but the bottom end looks like it was made by a master model engineer, and the top end by an amateur. I am trying to put right all the wrongs without having to make too many new parts.
I have most of the plans, but no instructions. So I am timing it by the seat of my pants, thru experiences of similar engines. It runs OK, but would just like to get it spot on, it is nearly there just not quite if you know what I mean. Or if anyone has the timing setup, a look at it would be gratefully appreciated.
John
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It is the Marcher, but the bottom end looks like it was made by a master model engineer, and the top end by an amateur. I am trying to put right all the wrongs without having to make too many new parts.
I have most of the plans, but no instructions. So I am timing it by the seat of my pants, thru experiences of similar engines. It runs OK, but would just like to get it spot on, it is nearly there just not quite if you know what I mean. Or if anyone has the timing setup, a look at it would be gratefully appreciated.
John
Hi John
I've got the original ME construction articles by John Bertinat for both Marcher and Borderer. If they'd be useful I could get them copied for you.
HTH
Guy